The gut reservoir of carbapenem-resistant Enterobacterales: from dysbiosis and colonization to infection and decolonization, with a focus on patients with hematologic malignancies - a narrative review

Carbapenem-resistant Enterobacterales (CRE) remain among the highest-priority antimicrobial-resistant pathogens worldwide, and intestinal colonization is increasingly recognized as the key precursor of invasive infections, particularly in patients with hematological malignancies. Increasing evidence indicates that disruption of the gut microbial ecosystem, reflected in reduced diversity, depletion of beneficial anaerobic taxa, intestinal barrier dysfunction, immune dysregulation, and expansion of Enterobacterales, plays a central role in the transition from colonization to infection. Consequently, restoring colonization resistance through microbiome-targeted interventions has emerged as a promising preventive strategy. This narrative review summarizes the current evidence on the epidemiology and clinical impact of CRE colonization and infection, with particular emphasis on the ecological alterations of the gut microbiome linking gut dysbiosis to epithelial barrier dysfunction, immune dysregulation, and loss of colonization resistance to CRE persistence and invasive infection. We critically discuss both conventional and emerging decolonization approaches, including selective digestive decontamination, probiotics, prebiotics and synbiotics, fecal microbiota transplantation (FMT), bacteriophage therapy, and CRISPR-Cas-based technologies, highlighting their mechanisms of action, available clinical evidence, and current limitations. Particular attention is given to patients with hematological malignancies, in whom the clinical need for effective decolonization strategies is greatest. Although FMT currently represents the most promising microbiome-based intervention, the available evidence remains heterogeneous and largely derived from small studies. Overall, durable and standardized decolonization strategies have yet to be established, underscoring the need for well-designed multicenter randomized clinical trials to define effective microbiome-directed approaches for preventing CRE-related infections in high-risk populations.